We have been able to prove the existence of a hypercalcemic factor in plasma of the rabbit with VX-2 carcinoma and to show that the material is excreted in the urine as a polypeptide with a molecular weight in the range of 5,000 to 15,000. The tumor produces a material or materials which is extractable and behaves biologically like parathyroid hormone but is produced at a much lower concentration than parathyroid hormone found in adenomatous human parathyroid tissue. The material is not signficantly immunoreactive with antibody reactive to beef parathyroid hormone or human parathyroid adenoma tumor extract. The progression of the hypercalcemia with hypophosphatemia in the tumor animal, with resultant uremia and death, very closely mimics the progress of events in man. The object of this proposal is to study this animal model, which seems to mimic the non-endocrine hormone producing cancer in man. The aim of this study is the isolation and characterization of the hypercalcemic polypeptide by use of bioassay procedures, purification studies with polyacrylamide and starch gel columns and an attempt to establish immunological identification of this material.